Previous experiments have revealed that nuclei of eukaryotic cells contain an enzyme which polymerises the ADP-ribose moiety of NAD through a 1'-2'-ribose-ribose linkage to form poly(ADP-ribose). The polymer is at least in part associated with basic chromosomal proteins and in particular histone H1. The current objective is to characterize the nuclear proteins to which poly(ADP-ribose) is attached with special emphasis on histone H1 and to elucidate the significance of this protein-poly(ADP-ribose) association in so far as nuclear processes during cellular growth is concerned. BIBLIOGRAPHIC REFERENCES: Stone, P.R., Lorimer, W.S. III, and Kidwell, W.R.: Proceedings of the 4th International Symposium on Poly(ADP-ribose) and ADP-ribosylation of Proteins. In Hilz, H. (Ed.), Walter De Gruyter, Berlin, N.Y., 1976, p.6. Hilz, H. and Stone, P.R.: Poly(ADP-Ribose) and ADP-ribosylation of proteins. Rev. Physiology, Biochemistry and Pharmacology 76: 1-58, 1976.